V4L/DVB (4132): Don't kill cx88 DMA sound on channel change

There's a call at cx88-tvaudio to reset DMA sound on channel change; that
call was killing cx88-alsa whenever the channel was changed, resulting
in no sound. Remove those calls if cx88-alsa is selected to be compiled.

Signed-off-by: Ricardo Cerqueira <v4l@cerqueira.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>